This invention relates to an apparatus for data transfer with interchangeable magnetic disks, particularly those of the class commonly referred to as "microfloppy disks," having a hub of magnetic material attached centrally thereto, as disclosed in Takahashi et al. U.S. Pat. No. 4,445,155 assigned to Sony Corp., of Tokyo, Japan. Still more particularly, the invention concerns a disk drive mechanism in such a data transfer apparatus for imparting rotation to the magnetic disk.
The prior art disk drive mechanism (shown in FIG. 1 of the drawings attached hereto) for use with magnetic disks of the type in question has a turntable of approximately the same size as the central hub of the magnetic disk to be mounted thereon. The turntable is mounted on a spindle which in fact may be the output shaft of an electric disk drive motor. Partly projecting from the turntable, the spindle is engageable in a central hole in the hub of the magnetic disk when the latter is coaxially placed upon the turntable. A spring biased, retractable drive pin is mounted eccentrically on the turntable for engagement in a slot defined eccentrically in the disk hub for transmitting the rotation of the turntable to the magnetic disk. Also mounted on the turntable is a permanent magnet for attracting the hub of ferromagnetic material at the center of the disk.
A problem has existed in connection with the permanent magnet of the prior art disk drive mechanism of the above construction. As the turntable is also of magnetic material, the magnet creates closed magnetic circuits in combination with the turntable and the hub of the magnetic disk on the turntable. The conventional construction of the disk drive mechanism has been such, however, that the magnetic lines of force due to the permanent magnet have been easy to partly leak through the gap between turntable and disk drive, as will be later explained in more detail. Such leakage flux is objectionable because it can adversely affect the process of data transfer between the magnetic disk and a transducer head or heads disposed on on one or both sides of the disk.